Rifamycin-Related Polyketides from a Marine-Derived Bacterium Salinispora arenicola and Their Cytotoxic Activity

Eight rifamycin-related polyketides were isolated from the culture broth of a marine-derived bacterium Salinispora arenicola, including five known (2–5 and 8) and three new derivatives (1, 6, and 7). The structures of the new compounds were determined by means of spectroscopic methods (HRESIMS and 1D, 2D NMR) and a comparison of their experimental data with those previously reported in the literature. The isolated compounds were evaluated for their cytotoxicity against one normal, six solid, and seven blood cancer cell lines and 1 showed moderate activity against all the tested cell lines with GI50 values ranging from 2.36 to 9.96 µM.